The present invention relates to a foam extinguishing system and more particularly to a foam extinguishing system which generates extinguishing foam containing non-combustible gases such as halogenated gas.
Hitherto known foam extinguishing systems of this kind comprise, as shown in FIG. 1, foam nozzles 3 of aspirator type at the rear part of a chamber 1 provided with a foam generating net 2 at the front, and gas discharge nozzle 7 to discharge non-combustible gas solution which generates halogenated gas, carbon dioxide gas, etc. at the rear of the chamber. Thus a non-combustible gas containing foam is generated by discharging a foam solution and a non-combustible gas solution from the foam nozzles 3 and the gas discharge nozzle 7, respectively.
In such a conventional system a considerable amount of the non-combustible gas solution G' discharged from the gas discharge nozzle 7 comes into contact and collides with the foam solution F as a liquid prior to its vaporization, resulting in the foam solution which has come into contact and collided with the liquid non-combustible gas is dispersed on the foam generating net 2 in a frozen state. A part of the non-combustible gas which has reached the foam generating net 2 in a liquid state also freezes a part of the foam solution dispersed over the foam generating net 2 in the same way. Consequently the foam generating efficiency is remarkably decreased and simultaneously the content of the non-combustible gas within the generated foam is reduced, resulting in lowering fire extinguishing capability.
It is possible to solve this problem by making the distance between the gas discharge nozzle 7 and the foam generating net 2 sufficiently long enough so that the non-combustible gas solution G' can be vaporised before it meets the foam solution F. However, this requires that the chamber 1 be remarkably lengthened, and the resultant increase in size of the system poses another problem in connection with its installation. To solve these problems it has been proposed to provide a heater 8, as shown in FIG. 1 with dotted lines, in front of the gas discharge nozzle 7 to heat the non-combustible gas solution G' discharged from the nozzle 7 and to forcedly vaporize it. However, use of the heater 8 which is liable to malfunction due to shorts in the heating coil necessitates frequent inspection. This also makes the constitution complicated, and therefore it is difficult to equalize the flow of air flow A inside the chamber (this also applies to the case where the heater 8 is arranged at the rear of nozzle 7), making the size of the generated foam uneven. Further new wiring for the heater 8 is needed.
It has also been proposed to provide a spray nozzle 9 at a position shown in FIG. 1 with dotted lines so that a non-combustible gas solution may be discharged in the form of mist. However, in this case such problems arise that the non-combustible gas solution discharged in a mist form is enveloped by the discharged flow of the foam solution F so that the concentration and distribution of the gas becomes uneven, the gas concentration contained in the foam varying greatly, and an optimum discharge pattern of the foam solution F being difficult to obtain because of the disturbance of the dicharge flow of the foam solution F caused by the discharge pressure of the non-combustible gas solution, or the clogging of the spray nozzle. Furthermore, in some cases there still remains a question of freezing of the foam solution.